Preparation And Characterization Of Anion Exchange Membranes Based On Fluorinated Poly(Aryl Ether Oxadiazole)s For AEMFCs Applications

Fuel cells convert the chemical energy of a reaction directly into electrical energy,have attracted considerable attention due to their high efficiency, high power density andenvironment friendly, are considered to be one of the most promising power supplydevices. Combined the advantages of PEMFCs with alkaline fuel cells, alkalineelectrolyte membrane fuel cells （AEMFCs） have been attracting widely interest. Whenchanging acidic medium into a basic one, AEMFCs have the potential to address manyproblems exist in PEMFCs while keeping higher power and energy density.The anion exchange membranes （AEMs） is the key component of fuel cells. It servesas the partition that separates the fuel from the oxidant and the support of catalyst. ForAEMFCs applications, AEMs should possess necessary conductivity, dimension stabilityand excellent solubility for MEA preparation. However, most of commercial AEMs cannot apply to AEMFCs for now. In order to obtain high performce AEMs for AEMFCs,we prepared two series of fluorinated poly（arylene ether-1,3,4-oxadiazole）s anionexchange membranes by copolymerization, functionalization by NBS and followingamination with trimethylamine and N-methyl imidazole, respectively. The detail workpresent as follows:1. A novel high molecular weight linear polymer were synthesized via thecopolymerization of tetramethyl bisphenol A（TM-BPA） and2,5-bis（2,3,4,5,6-pentafluorophenyl）-1,3,4-oxadiazole （FPOx） at mild condition such as roomtemperature, K₂CO₃as catalyst. The molecular weight and distribution of the copolymerswere studied at different reaction time. The brominated polymers were obtained byfunctionalization with NBS, the degree of functionality （DF） was investigated by theamout of NBS used. The chemical structures of the resulting polymers were confirmed byNMR, FT-IR and GPC.2. A series of fluorinated poly（aryl ether oxadiazole）s ionomer with pendantquaternary ammonium groups （QFPAEO-x） having different IECs were prepared byhomogeneous amination of bromomethylated poly（aryl ether oxadiazole）s（FPAEO-xBrTM） with varying DFs in trimethylamine/DMF/water solution. Therelationships between structures and properties of the QFPAEO-x membranes, such ashydroxide conductivity, water uptake and swelling ratio, were studied in detail.3. To further improving the conductivity, a series of anion exchange membranesbased on imidazolium salts （FPAEO-xMIM） were prepared by quaternization of FPAEO-xBrTM using N-methyl imidazole as amination reagent, casting in DMF solutionand followed by hydroxide exchanging in aqueous sodium hydroxide. The structure of theresulting polymers was characterized and confirmed with1H NMR and FT-IRmeasurements. The physical and electrochemical properties of anion exchangemembranes （AEMs） were studied. The hydroxide conductivity of FPAEO-xMIMmembranes were almost higher than10^-2S cm^-1at room temperature, while the wateruptake and swelling ratio were moderate even at elevated temperature. TGA revealed thatAEMs based on imidazolium salts had good thermal stability.Moreover, all the anion exchange membranes exhibited high solubility inlow-boiling point solution, such as methanol, which is facilitated MEA fabricating. Theresults show that the prepared two series anion exchange membranes have goodperspectives and great potential for AEMFCs applications.